Configurable voltage regulator

ABSTRACT

A voltage regulator having a device characteristic comprises a first terminal connectable to a first external impedance. A measurement circuit communicates with the first terminal to measure the first external impedance. A control circuit controls the device characteristic as a function of the measured first external impedance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/411,377 filed Apr. 26, 2006, which is a divisional of U.S. patentapplication Ser No. 11/220,255, filed on Sep. 6, 2005, now U.S. Pat. No.7,062,392, which is a divisional of application Ser. No. 10/251,372,filed Sep. 19, 2002, now U.S. Pat. No. 6,970,794, the entire contents ofwhich are herein incorporated by reference.

BACKGROUND

Broad classes of semiconductor devices may include severalconfigurations of the same basic device differing in one or more aspectssuch as output voltage, frequency, trigger temperature, and the like.There are several conventional techniques for providing a specificconfiguration from a family of devices. In one technique, differentversions of the same basic semiconductor are manufactured with slightlydifferent internal component values or configuration to provide thediffering outputs. For example, voltage regulators may include a familyof devices having various output voltages and tolerance levels.Different devices are manufactured and inventoried by suppliers etc. toprovide each of the possible combinations of output voltage andtolerance. An advantage of this approach is that devices with tighttolerances may be provided without the need for expensive externalcomponents. However, the cost of the regulators may be higher due to thelower quantities that are produced for each specific voltage/tolerancecombination as well as the increased inventory costs.

Another technique uses one or more external components to complete aninternal circuit such as an error amplifier for a voltage regulator.Here, the tolerance of the external components has a direct affect onthe tolerance of the output that is generated. To attain an output witha tight tolerance, higher priced tight tolerance external components maybe required. In addition, a large selection of the tight toleranceexternal components may be have to be stocked to provide flexibility insetting the output to the desired value.

Shown in FIG. 1A is a third technique for configuring a semiconductor 5.The third technique uses digital input signals to set the semiconductorconfiguration. Pull-up resistors 6 in combination with switches 7generate the digital input signals. One digital input may select betweentwo (2 ¹) configurations. Two digital inputs may select between four (2²) configurations. Three digital inputs may select between eight (2 ³)configurations and so on. To select between a moderate number ofconfigurations, a large quantity of pins may be required. Dedicatingfour pins merely for selecting between 16 configurations is costly interms of both, price and package size. Whereas, using two pins forselection may provide reasonable cost and package size, but onlyprovides selection from amongst four configurations.

SUMMARY

A voltage regulator has a plurality of predetermined configurations andcomprises a measurement circuit to measure an electrical characteristicof at least one external impedance and to determine a digital valuecorresponding to the measured electrical characteristic. An addressgenerator converts the digital value to a first digital addresscorresponding to a memory location having contents. Each of the contentscorresponds to a respective one of the predetermined configurations. Acontroller configures the voltage regulator based on the contents of thememory location corresponding to the first digital address.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1A is a block diagram of a selection circuit connected to aconventional configurable semiconductor.

FIG. 1B is a block diagram of a configurable semiconductor connected toexternal impedances.

FIG. 2 is a detailed block diagram of a configurable semiconductorconnected to external impedances.

FIGS. 3A and 3B are diagrams showing a relationship between an externalimpedance value and a digital value.

FIG. 4 is a schematic diagram of a configurable semiconductor having amultifunction pin.

FIG. 5 is a schematic diagram of a multifunction pin with programmablecontrol.

FIG. 6 is a schematic diagram of a timing circuit for generating adigital value.

FIG. 7 shows waveforms associated with the timing circuit of FIG. 6.

FIG. 8 is a flow diagram of an operation for configuring asemiconductor.

FIG. 9 is a flow diagram of an operation for selecting values forexternal impedances for configuring a semiconductor.

FIG. 10A is a block diagram of a voltage regulator connected to anexternal impedance.

FIG. 10B is a block diagram of a voltage regulator connected to twoexternal impedances.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1B shows a configurable semiconductor device 10 having, forexample, two select pins 12 and 14 to connect to two external impedances16 and 18. The configurable semiconductor device 10 advantageously usesa reduced number of select pins for interfacing to external components,as compared to conventional devices, to select one or more output andinternal characteristics. One or more pins may be used to interface tothe external component(s). The configurable semiconductor device probesor derives information from the external components connected to theselect pins. The derived information has three or more predeterminedlevel ranges that correspond to selected levels of the devicecharacteristics. For example, a single pin connected to an externalresistor may be used to select any one of 16 output voltage levels. Theresistance of the external resistor is preferably selected to be one of16 predetermined standard values. Each of the 16 values of resistancecorresponds to one of the 16 output voltage levels. In addition, lowprecision passive components are preferably used as the externalcomponents to reduce cost and inventory. Each external component mayhave multiple, N, predetermined nominal values that each correspond tothe selection of a predetermined characteristic level. If one pin isused, then N different characteristic levels may be selected. If twopins are used, then N*N different characteristic levels may be selected,and so forth for an increasing number of selection pins. The types ofdevice characteristics that for example may be selected include outputvoltage, reference voltage, output current, reference current, clockfrequency, temperature threshold, and tolerances of each of the devicecharacteristics. For example, the configurable semiconductor device 10may have a single select pin 12 connected to an external resistor thatmay have a nominal value selected from a group of 16 predeterminedvalues. Each of the 16 predetermined values has a measured value rangewhich corresponds to one of 16 predetermined output voltage levelspossibly ranging from 3.3 volts to 15 volts. Examples of functionaldevices for which the configurable semiconductor device is particularlysuitable include and are not limited to voltage regulators, currentregulators, clock circuits, and temperature sensing circuits.

The external impedances 16 and 18 are preferably resistors, capacitors,or combinations of resistors and capacitors, but may be any componentthat exhibits predominantly an inductance, resistance, capacitance, orcombination thereof. The external impedances 16 and 18 may be connecteddirectly or indirectly from any energy source such as Vdd and ground orany suitable reference to the configurable semiconductor device pins 12and 14. For example, the external impedance 16 may be connected througha resistor/transistor network to Vdd and through a capacitor network tothe select pin 12.

The configurable semiconductor device 10 may determine a predeterminedselect value corresponding to the measured value of the impedanceconnected to a select pin. Preferably, the impedance is selected to havea standard value such as nominal resistance values corresponding toresistors having a 10% tolerance (e.g. 470, 560, 680, . . . ) to reducedevice and inventory costs. To account for measurement tolerances andthe tolerance of the external impedance, a range of impedance values maycorrespond to a single select value. The select value is preferably adigital value, but may also be an analog value. For example, values ofmeasured resistance from 2400 ohms to 3000 ohms may be associated with adigital value corresponding to 2. While values of measured resistancefrom 3001 ohms to 4700 ohms are associated with a digital valuecorresponding to 3. The measured resistance includes variations due totolerances of the external impedance and the internal measurementcircuit. The impedance measured at each select pin is used to determinea corresponding digital value. The range of digital values may include 3or more digital values and preferably range from 10 to 16 digital valuesper select pin. The digital values corresponding to each select pin maybe used in combination to describe memory addresses. For example, adevice having three select pins each to interface to impedance valuesthat are mapped into one of 10 digital values, may describe 1000 memoryaddresses or lookup table values. The contents of the memory addressesare used to set a value for an output or internal characteristic of thedevice. Another exemplary device may include two select pins, eachconfigured to interface to external impedances that are mapped to adigital value within a range of 10 values. The digital values incombination may describe 100 memory addresses or lookup table valuesthat may each contain data for setting a characteristic of theconfigurable semiconductor device.

FIG. 2 shows a block diagram of an aspect of a configurablesemiconductor device 20. The configurable semiconductor device 20includes a select pin 22 to interface to an external impedance 24 thatis used for selecting a configuration of the configurable semiconductordevice 20. The external impedance 24 is similar in function and scope tothe external impedances 16 and 18.

A measurement circuit 26 connected to the select pin 22 measures anelectrical characteristic that is a function of the external impedance24. For example, a current may be supplied to the external impedance andthe voltage that is developed across the external impedance 24 thenmeasured. Also, a voltage may be impressed across the external impedance24 and then measure the current. Any measurement technique for measuringpassive components may be used to measure the electrical characteristicincluding dynamic as well as static techniques. Exemplary measurementtechniques include timing circuits, analog to digital converters (ADCs),and digital to analog converters (DACs). Preferably, the measurementcircuit has a high dynamic range. The measurement circuit 26 maygenerate an output having a value corresponding to the value of theexternal impedance 24. The output may be either digital or analog. Thesame output value preferably represents a range of external impedancevalues to compensate for value variations such as tolerances in theexternal impedance value, interconnect losses, and measurement circuittolerances due to factors including process, temperature, and power. Forexample, all measured external impedance values ranging from greaterthan 22 up to 32 ohms may correlate to a digital output value of “0100”.While measured external impedance values ranging from greater than 32 upto 54 ohms may correlate to a digital output value of “0101”. The actualexternal impedance values are a subset of the measured externalimpedance value to account for the value variations. For example, in theabove cases the actual external impedance values might be from 24 to 30ohms and from 36 to 50 ohms. In each case an inexpensive low precisionresistor may be selected to have a value centered within the range, suchas 27 ohms and 43 ohms. In this way, inexpensive low precisioncomponents may be used to select amongst a range of high precisionoutputs. The select value may be used directly as a variable value tocontrol a device characteristic of the configurable semiconductor 20.The variable value may also be determined indirectly from the selectvalue.

A storage circuit 27 may include variable values that may be selected asa function of the select value. The storage circuit may be any type ofstorage structure including content addressable memory, static anddynamic memory, and look-up tables.

For the case that the measurement circuit 26 generates output valuesthat have a one-to-one correspondence to the external impedance values,a digital value determiner 28 may then set the output value to a selectvalue that corresponds to a range of external impedance values.

FIG. 3A shows a relationship between groups of impedance values 50 andassociated select values 54. The groups of impedance values 50 may havea one-to-one correspondence to groups of digital output values 52 whichare converted to the select values 54 associated with each of the groupsof impedance values 50. The impedance values ranging from a minimumimpedance value to a maximum impedance are separated in into three ormore groups, with each group having a nominal impedance. The nominalimpedance values of each of the groups may be selected to have a spacingbetween nominal impedance values. Here, the nominal values, 27 ohms and43 ohms, of the groups of impedance values have a spacing of 16 ohms.The spacing between the groups of impedance values is preferably basedon geometric progression, however any mathematical relationship may beused to establish spacing between the groups such as logarithmic,linear, and exponential. The spacing between impedance groups may bebased on any impedance value of the groups including a nominal value, anaverage value, a mean value, a starting value, and an ending value.Factors that influence selection of the impedance range of the groupsand the spacing may include various tolerances such as the tolerance ofthe external impedance, the tolerance of internal voltage and currentsources, and the tolerance of the measurement circuit. The tolerancesmay for example be caused by process, temperature, and power variations.

FIG. 3B shows a relationship between ranges of impedance values 56 andassociated select values 58. The ranges of impedance values 56 have adirect correspondence to the select values 58. The impedance valuesranging from a minimum impedance value to a maximum impedance areseparated in into three or more groups, with each group having a nominalimpedance. The nominal impedance values of each of the groups may beselected to have a spacing between nominal impedance values. Here, thenominal values, 27 ohms and 43 ohms, of the groups of impedance valueshave a spacing of 16 ohms. This direct correspondence between the rangesof impedance values 56 and associated select values 58 may beimplemented by, for example, a nonlinear analog to digital converter(not shown).

Referring back to FIG. 2, an address generator 30 may determine memorylocations corresponding to the digital output values associated withexternal impedances connected to the select pins. The memory locationsmay be grouped in any manner such as a list for a single select pin, alookup table for two select pins, and a third order table for threeselect pins.

A controller 32 sets a device characteristic of the configurablesemiconductor device 20 as a function of the variable value. Thevariable value may be generated directly by the measurement circuit,determined indirectly from the select value, and determined from thecontents of a memory location corresponding to the external impedancevalues connected to the select pins.

FIG. 4 shows an aspect of another configurable semiconductor device 60.Configurable semiconductor device 60 is similar to configurablesemiconductor device 20 in function, except that configurablesemiconductor device 60 includes at least one multi-purpose select pin62. The multi-purpose select pin 62 may be used for configuring thesemiconductor device 60 as well as for an additional function such aspower down (PD), power enable, mode selection, reset, and synchronousoperation. The semiconductor device 60 may be configured in a mannersimilar to that of configurable semiconductor device 20.

In one aspect, a first range of impedance values connected to themulti-purpose select pin 62 may be used to configure the configurablesemiconductor device 60, while operation of the additional function maybe controlled by a voltage or current impressed on the multi-purposeselect pin, or impedance values outside the first range of impedancevalues.

An external impedance 64 and a switch 66 may be connected to themulti-purpose select pin 62 to provide the selection function and theadditional function respectively. Bias voltages, Vb1 and Vb2, may beapplied to the external impedance 64 and transistor 66. The biasvoltages, Vb1 and Vb2, may each be any value ranging from negativevoltage through ground to positive voltage, and equal or not equal. Theswitch 66 may be connected in any manner including from themulti-purpose select pin 62 to ground, from the multi-purpose select pin62 to a voltage source, from the multi-purpose select pin 62 to acurrent source, and from the multi-purpose select pin 62 through anotherimpedance to an energy source. Any type of switch or device configuredas a switch may be used including transistors, analog switches, jumperwires/traces, and manual switches.

FIG. 5 shows a configurable semiconductor device 70 coupled to a digitalcontrol circuit 72. The digital control circuit 72 may be connected inany manner such as a stand-alone circuit and included in another devicesuch as a processor. The configurable semiconductor device may include amulti-purpose select pin 74 similar in function to configurablesemiconductor device 60. The digital control circuit 72 may includeseveral switches 76 to control external impedances 78 for setting animpedance on the multi-purpose select pin 74. Any number and type ofswitches 76 may be employed including transistors, analog switches,jumper wires/traces, and manual switches. Preferably, the externalimpedances 78 are selected to have standard values although any range ofvalues may be used. Another transistor 80 may control operation ofadditional functions.

FIG. 6 shows one embodiment of a measurement circuit 100 for determininga digital output 106 corresponding to an external impedance 102. Theexternal impedance 102 may be connected to the measurement circuit 100through a select pin 104. Table I shows exemplary values for theexternal impedance 102 and corresponding values of the digital output.Predefined operation #2 may enable the power down function. Theimpedance at the select pin that corresponds to predefined operations #1or #2 may be intentional or unintentional such as a selected resistor, acold solder joint, a broken trace, shorted traces, or a failed externaldevice.

TABLE I Digital # Rx/Ry Vout Vout % Output 0 Short to Vss up 0 0Predefined to 10k operation #1 1 19.6k  0.8 −2 000 2 28.5k  1.0 −4 001 3 40k 1.2 −6 010 4  56k 1.5 −8 011 5 80.6k  1.8 +2 100 6 113k 2.5 +4 1017 160k 3.0 +6 110 8 226k 3.3 +8 111 9 400k to an open Predefinedoperation #2

FIG. 7 shows a timing diagram associated with the measurement circuit100. A first waveform 120 represents a clock signal 120 to the Dflip-flop 110. A second waveform 122 represents an input signal to the Dinput of the flip-flop 110. In operation, a controlled resistor 112 isinitially set to a predetermined value. A first voltage is developed ata first node 114 as a function of the controlled resistor 112 and theexternal impedance 102. The first voltage is clocked through theflip-flop 110 by the clock signal 120. An incrementer/decrementer 116may convert the output of the flip-flop 110 to the digital output 106.In response to the digital output 106, a decoder 118 adjusts thecontrolled resistor 112 to decrease the first voltage. The countercontinues to increment until the first voltage decreases to a levelequivalent to a logic “0”.

FIG. 8 shows an operation of a configurable semiconductor device.Starting at block 150, energy is supplied to an external impedance.Continuing to block 152, an electrical characteristic that is a functionof the external impedance is measured. Electrical characteristics suchas a voltage at the select pin and a current flowing through the selectpin may be measured. At block 154, a select value corresponding to themeasured electrical characteristic is determined. Continuing to block156, an address may be generated as a function of the digital value. Atblock 158, the contents of the address are determined. At block 160, avariable may be controlled as a function of the select value such asdirectly and based on the address contents. At block 162, a devicecharacteristic such as an output voltage may be controlled as a functionof the variable.

FIG. 9 shows an operation for selecting the spacing of externalimpedances used for configuring a semiconductor device. The spacing ispreferably selected to permit the use of low precision components byvarying the spacing from lower values to higher values to account forpotential variations associated with the measurement circuit. Startingat block 200, a measurement circuit is provided. Continuing to blocks202 and 203, tolerances associated with the measurement circuit and theexternal impedances may be determined. The tolerances may includevariations due to process, temperature, and power. At block 204, ameasurement error such as a geometric progression, a maximum error, androot of the sum of the squares (RSS) error may be computed. Continuingto block 206, a quantity of discrete values for the external impedancemay be determined. For example, the measurement error may be appliedacross a voltage range of the measurement circuit to determine themaximum number of discrete values that may be selected. The quantity ofdiscrete values may be any integer value greater than one. At block 208,nominal values are selected for the external impedance as a function ofthe computed error and the selected quantity of discrete values. Thedescribed operation is not limited to the described order of operation.Other ones of the variables may be solved for such as solving for thetolerance of the external impedance after selecting a desired quantityof discrete values.

FIG. 10A is an example of a voltage regulator in accordance with thepresent invention. Referring now to FIG. 10A a voltage regulator 200 isshown therein providing Vout to load 210, an external impedance 220 isused to select Vout. Table II shows exemplary values for the externalimpedance 220 and corresponding values of Vout. Predefined operation #2may enable the power down function or low voltage to protect for anovervoltage condition presented to load 210. The impedance at the selectpin that corresponds to predefined operations #1 or #2 may beintentional or unintentional such as a selected resistor, a cold solderjoint, a broken trace, shorted traces, or a failed external device.

TABLE II # Impedance 220 Vout 0 Short to Vss up 0 or power to 10k down 119.6k  0.8 2 28.5k  1.0 3  40k 1.2 4  56k 1.5 5 80.6k  1.8 6 113k 2.5 7160k 3.0 8 226k 3.3 9 400k to an open 0 or low voltage

FIG. 10B is an example of a voltage regulator in accordance with thepresent invention. Referring now to FIG. 10B a voltage regulator 200 isshown therein providing Vout to load 210, an external impedance 220 isused to select a nominal Vout and impedance 240 is used to select theoffset from the nominal Vout. This provides for a significant number ofadditional output voltages. Table III shows exemplary values for theexternal impedance 220 and corresponding values of the offsetpercentages. If impedance 240 is a large value or perhaps an opencircuit no offset will be applied to the nominal Vout. While ifimpedance 240 is a short or very low a predefined operation, such asdiscussed above, is implemented.

TABLE III Offset # Impedance 240 percentage 0 Short to Vss up Predefinedto 10k operation 1 19.6k  −2 2 28.5k  −4 3  40k −6 4  56k −8 5 80.6k  +26 113k +4 7 160k +6 8 226k +8 9 400k to an open No Offset

TABLE IV Short to Vss up to 10k 19.6k 28.5k 40k 56k 80.6k 113k 160k 226k400k to Imped Imped Nominal Offset % an 240 220 Vout 0 −2 −4 −6 −8 +2 +4+6 +8 open Short 0 or 0 or 0 or 0 or 0 or 0 or 0 or 0 or 0 or 0 or 0 or0 or toVss power power power power power power power power power powerpower power up to down down down down down down down down down down downdown 10k 19.6k  0.8 0.8 * 0.784 0.768 0.752 0.736 0.816 0.832 0.848.0864 0.8 28.5k  1.0 1.0 * 0.980 0.960 0.940 0.920 1.020 1.040 1.0601.080 1.0  40k 1.2 1.2 * 1.176 1.152 1.128 1.104 1.224 1.248 1.272 1.2961.2  56k 1.5 1.5 * 1.470 1.440 1.410 1.380 1.530 1.560 1.590 1.620 1.580.6k  1.8 1.8 * 1.764 1.728 1.692 1.656 1.836 1.872 1.908 1.944 1.8113k 2.5 2.5 * 2.450 2.400 2.350 2.300 2.550 2.600 2.650 2.700 2.5 160k3.0 3.0 * 2.940 2.880 2.820 2.760 3.060 3.120 3.180 3.240 3.0 226k 3.33.3 * 3.234 3.168 3.102 3.036 3.366 3.432 3.498 3.564 3.3 400k 0 or 0 or0 or 0 or 0 or 0 or 0 or 0 or 0 or 0 or 0 or 0 or to an low low low lowlow low low low low low low low open voltage voltage voltage voltagevoltage voltage voltage voltage voltage voltage voltage voltage *predefined operation

Table IV above is an example of the nominal Vout and the offsetpercentage selected in accordance with external impedances. For exampleif impedance 220 is nominally 160 k ohms the nominal Vout is 3.0 voltsand if impedance 240 is 28.5 k the offset from the nominal Vout is −4%.This results in a Vout of the voltage regulator of 3.168 volts.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

1. A voltage regulator having a device characteristic, comprising: afirst terminal connectable to a first external impedance; a secondterminal connectable to a second external impedance; a measurementcircuit in communication with the first and second terminals to measurethe first and second external impedances; and a control circuit tocontrol the device characteristic as a function of the measured firstexternal impedance and to control an offset as a function of themeasured second external impedance.
 2. The voltage regulator of claim 1further comprising an address generator to convert the measured firstexternal impedance to a first address corresponding to a memory locationhaving contents; and wherein said control circuit controls the devicecharacteristic as a function of the contents of the memory locationcorresponding to the first address.
 3. The voltage regulator of claim 1further comprising a generator in communication with the first terminalto supply energy to the first external impedance.
 4. The voltageregulator of claim 1 wherein the measurement circuit is selected from agroup consisting of timing circuits, Digital to Analog Converters, andAnalog to Digital Converters.
 5. The voltage regulator of claim 1further comprising a value determiner to determine a digital valuecorresponding to the measured device characteristic.
 6. The voltageregulator of claim 1 wherein the first external impedance is selectedfrom a group consisting of a resistor, a capacitor, and combinationsthereof.
 7. A voltage regulator having a device characteristic,comprising: a first terminal connectable to a first external impedance;a measurement circuit in communication with the first terminal tomeasure the first external impedance; a control circuit to control thedevice characteristic as a function of the measured first externalimpedance; and a second terminal connectable to a second externalimpedance; wherein the measurement circuit is in communication with thesecond terminal and measures the second external impedance, wherein themeasured first external impedance corresponds to a nominal outputvoltage and the measured second external impedance corresponds to the anoutput voltage offset, and wherein the output voltage is a function ofthe nominal output voltage and the output voltage offset.
 8. The voltageregulator of claim 1 wherein the first external impedance value isselected from a predetermined group of values comprising at least threevalues.
 9. The voltage regulator of claim 8 wherein the group of valueshas a spacing characteristic selected from a group consisting ofgeometric progression, exponential, linear, and logarithmic.
 10. Thevoltage regulator of claim 8 wherein the at least three values are eachnominal values; and wherein the at least three nominal values are spacedapart based on tolerances associated with at least the measurementcircuit.
 11. The voltage regulator of claim 8 wherein the devicecharacteristic is selected from a group consisting of output voltage,reference voltage, output current, reference current, output frequency,reference frequency, and temperature level.
 12. A voltage regulatorhaving a device characteristic, comprising: a first input means forcommunicating with a first external impedance; second input means forcommunicating with a second external impedance; measurement means forindependently measuring the first and second external impedances; andcontrol means for controlling the device characteristic as a function ofthe measured first external impedance and to control an offset as afunction of the measured second external impedance.
 13. The voltageregulator of claim 12 further comprising an address generator means forconverting the measured first external impedance to a first addresscorresponding to a memory location having contents; and wherein saidcontroller controls the device characteristic as a function of thecontents of the memory location corresponding to the first address. 14.The voltage regulator of claim 12 further comprising generator means incommunication with the first input means for supplying energy to thefirst external impedance.
 15. The voltage regulator of claim 12 whereinthe measurement means is selected from a group consisting of timingcircuits, Digital to Analog Converters, and Analog to DigitalConverters.
 16. The voltage regulator of claim 12 further comprisingvalue determiner means for determining a digital value corresponding tothe measured device characteristic.
 17. The voltage regulator of claim12 wherein the first external impedance is selected from a groupconsisting of a resistor, a capacitor, and combinations thereof.
 18. Avoltage regulator having a device characteristic, comprising: firstinput means for communicating with a first external impedance;measurement means for measuring the first external impedance; controlmeans for controlling the device characteristic as a function of themeasured first external impedance; and a second input means forcommunicating with a second external impedance; wherein the measurementmeans measures the second external impedance, wherein the measured firstexternal impedance corresponds to a nominal output voltage and themeasured second external impedance corresponds to the an output voltageoffset, and wherein the output voltage is a function of the nominaloutput voltage and the output voltage offset.
 19. The voltage regulatorof claim 12 wherein the first external impedance value is selected froma predetermined group of values comprising at least three values. 20.The voltage regulator of claim 19 wherein the group of values has aspacing characteristic selected from a group consisting of geometricprogression, exponential, linear, and logarithmic.
 21. The voltageregulator of claim 19 wherein the at least three values are each nominalvalues; and wherein the at least three nominal values are spaced apartbased on tolerances associated with at least the measurement means. 22.The voltage regulator of claim 19 wherein the device characteristic isselected from a group consisting of output voltage, reference voltage,output current, reference current, output frequency, referencefrequency, and temperature level.
 23. A method of selecting a devicecharacteristic of a voltage regulator, comprising the steps of:communicating with a first external impedance; communicating with asecond external impedance; measuring the first and second externalimpedances; and controlling the device characteristic as a function ofthe measured first external impedance and controlling an offset as afunction of the measured second external impedance.
 24. The method ofclaim 23 further comprising the steps of: converting the measured firstexternal impedance to a first address corresponding to a memory locationhaving contents; and controlling the device characteristic as a functionof the contents of the memory location corresponding to the firstaddress.
 25. The method of claim 23 further comprising the step ofsupplying energy to the first external impedance.
 26. The method ofclaim 23 wherein the measuring set is selected from a group consistingof generating a timing signal, converting a digital signal to an analogsignal, and converting an analog signal to a digital signal.
 27. Themethod of claim 23 further comprising the step of determining a digitalvalue corresponding to the measured device characteristic.
 28. Themethod of claim 23 wherein the first external impedance is selected froma group consisting of a resistor, a capacitor, and combinations thereof.29. A method of selecting a device characteristic of a voltageregulator, comprising the steps of: communicating with a first externalimpedance; communicating with a second external impedance; measuring thefirst and second external impedances; and controlling the devicecharacteristic as a function of the measured first external impedance,wherein the measured first external impedance corresponds to a nominaloutput voltage and the measured second external impedance corresponds tothe an output voltage offset, and wherein the output voltage is afunction of the nominal output voltage and the output voltage offset.30. The method of claim 23 wherein the first external impedance value isselected from a predetermined group of values comprising at least threevalues.
 31. The method of claim 30 wherein the group of values has aspacing characteristic selected from a group consisting of geometricprogression, exponential, linear, and logarithmic.
 32. The method ofclaim 30 wherein the at least three values are each nominal values; andwherein the at least three nominal values are spaced apart based ontolerances associated with at least the measurement means.
 33. Theregulator method of claim 30 wherein the device characteristic isselected from a group consisting of output voltage, reference voltage,output current, reference current, output frequency, referencefrequency, and temperature level.